The primary historical objective of waste water treatment operations has been to neutralize and otherwise render sewage effluence in compliance with regulatory limits based on environmental and health standards. An important and growing objective of modern waste water treatments is the generation of energy from biologically-digestible organic materials present in the waste water. To achieve this objective, during the treatment of waste water influent streams containing biologically-digestible materials, as part of selectively classifying and separating grits, solids, hair and fibers, particulates, and solvated materials, it is particularly desirable to separate the digestible materials in the influent stream from non-digestible materials such that digestion of the digestible materials can be optimized. For systems that produce sludge in processes downstream from primary clarification (i.e., secondary sludge), it is desirable to extract the remaining biologically-digestible materials present in that sludge. Optimization can include increasing and capturing the bio-gas producing materials; production of energy bearing bio-gasses such as methane, produced by the decomposition of the digestible materials; reducing the frequency with which digesters used to digest the digestible materials need to be taken off line and cleaned; automation of the process for separating the digestible materials in the influent stream for digestion to reduce operating costs; reducing energy consumption-related operating costs; reducing the particle size of organic materials to allow rapid biodegradation and to capture organics prior to conversion to carbon-dioxide and biomass; and reducing the capital costs to build a treatment facility to separate and digest biologically-digestible materials in an influent stream.
In the prior art, the separation of grit from waste water influent is a long standing problem. Grit adversely impacts equipment reliability and lifespan, and increases operating costs of downstream treatment processes. Consequently, grit separators traditionally are used to remove grit from the influent stream as early in the treatment sequence as possible, preferably prior to primary clarification, or in cases where no primary clarification exists, then prior to secondary treatment. In practice, these devices often perform poorly because they are designed for a specific flow range which often is based on peak flows based on projected increases in population or a specific maximum flow based on storm events or future expansion of flows from new industries, etc. The projected flow range frequently is not reached for a number of reasons, such as unanticipated changes in population; changes in economic conditions of a region causing industries to leave or never develop; increased inflow and infiltration (“I and I”) of water into the treatment system from deteriorating collection systems; and the increase in storm intensities.
In many treatment plants, in an attempt to provide flow equalization at the head of the plant, variable frequency drives have been added to control the pumps delivering influent to the treatment plants from wet wells used as buffers. The variable frequency drives enable operation of the pumps over a range of pump speeds rather than a single speed with the only control option being to turn them off and on. In practice, these variable frequency drives create large fluctuations in influent velocity that can hinder the performance of the highly velocity-sensitive hydrocyclone grit separators. Due to their poor performance, these velocity sensitive grit separators often fail and/or are left in disrepair, requiring grit to be removed from the influent stream as a component of the sludge formed during the primary-treatment process. Typically, the grit slowly fills the secondary treatment process tanks, contributing to reduced energy content of the primary sludge, increasing the frequency with which digesters and secondary process tanks must be cleaned, and causing wear and tear on the plant equipment.
Current typical waste water plants capture only thirty to thirty-five percent of the biologically-digestible materials during primary clarification. The remainder of the biologically-digestible materials are typically digested during secondary treatment in an activated sludge process that permits the greenhouse gas (CO2) to escape into the atmosphere.